Facebook's aim, according to its website, is to create "greater understanding and connection" by making "the world more open and transparent." Smitha Ballyamanda found out what that benign-sounding ambition could mean in 2006, when her ex-boyfriend's girlfriend began stalking her on the social networking site.

The situation started out simply enough. Ballyamanda, then a 23-year-old medical student in Miami, got repeated "friend" requests from the woman. Hoping to stop further contact, Ballyamanda blocked the woman from seeing her Facebook profile. But things only got worse. Her stalker created false accounts to befriend Ballyamanda and her friends. Then she hacked Ballyamanda's Hotmail and Facebook accounts and began sending bizarre e-mails to Ballyamanda's friends, family, and most embarrassingly, professional contacts. One message said that Ballyamanda was dropping out of medical school because she was pregnant. "I had my entire world turned upside down," Ballyamanda says.

As she regained control of her online identity, Ballyamanda deactivated her Facebook account. But she had second thoughts when she realized she'd cut her social lifeline. "That was my way of keeping in touch with people," says Ballyamanda, now a resident in family medicine in Philadelphia. Eventually she created a new account. But this time she read the fine print: She studied Facebook's privacy controls, and then she created an elaborate system to control what her contacts could see—and, more important, what they couldn't.

Countless such privacy-related minidramas have already played out behind the scenes of the world's largest social network. Now, with hundreds of millions of users, and firms like Google eager to take on Facebook with social networks of their own, it's a good time to ask: How many of us are ready for total transparency?

Transparency, in this case, means widely revealing personal details that you might ordinarily share with just a small subset of people. "Facebook is driving this idea that they want us to live more public lives," says Alice Marwick, a social media researcher at Microsoft Research New England, in Cambridge, Mass. In The Facebook Effect, a recent history of the social network, Facebook creator Mark Zuckerberg told author David Kirkpatrick that he envisions a society in which "you have one identity"—where "having a different image for your work friends or coworkers and for the other people you know" will no longer be possible or even desirable.

But this vision of a world full of indiscriminate sharing is not realistic, Marwick says: "We've always wanted to provide different types of information to different groups of people." For Ballyamanda, keeping those different groups apart now defines her Facebook experience.

Born in south India, Ballyamanda has good reason to keep some information private. Many of her relatives, especially older ones, have conservative views about how a young woman should behave.

Ballyamanda, a petite beauty with thick black hair and big brown eyes, isn't shy about wearing clothes that flatter her figure. Like most young professionals, she socializes in bars and clubs with friends of both sexes. But she frets that a Facebook photo of herself and a male coworker having an innocent after-work drink could ricochet among her far-flung family members and blossom into a story with no basis in reality: "You're getting married and that was your engagement party," as she puts it.

To control who sees her profile information, Ballyamanda has assigned each of her 682 Facebook friends to one of six groups. At the bottom of the heap is "Zero Trust." This group can't access old status updates, messages from her friends, or many of her photo albums. At the top of the heap are the 10 or 15 people who constitute the "Inner Circle." "They have full-blown access," she says. "They see my page as I would see it."

The system "makes me seem completely nuts," Ballyamanda concedes. "But that's how I protect myself in this new world where everyone can see everything." —Smitha Ballyamanda

In between are groups with intermediate levels of access. Those in either the "Coworker" or one of two "Guilty by Association" groups can see more of her profile than those in Zero Trust. And the "Paparazzi"—Ballyamanda's catch-all group for acquaintances and friends who haven't made the Inner Circle—can see a bit more still. Paparazzi members can see far more than Ballyamanda's own mother, who has been relegated to Zero Trust. "I tell her most of what's going on in my life," Ballyamanda says. "But I don't think she could handle the weight of my entire page."

If you ask her, Ballyamanda will tell you which group each of her contacts belongs to and why. Her cousin's wife, for example, should be in the Paparazzi. The two women are close. But then she would have access to sensitive information—photos of Ballyamanda drinking and wearing revealing clothes. If the woman ended up showing those photos to her husband, Ballyamanda's cousin and a member of Zero Trust, he might say something to the rest of her family. So Ballyamanda had no choice but to put his wife in Guilty by Association.

The system "makes me seem completely nuts," Ballyamanda concedes. "But that's how I protect myself in this new world where everyone can see everything."

This need to present different personas to different people is natural, says Microsoft's Marwick. "When you're in a job interview, you're presenting a different self than you are when you're at a bar with your friends," she says. "This is just logical." Your future boss doesn't need to know that you like tequila or tattoos.

But Facebook doesn't automatically distinguish among family, friends, and colleagues. Everyone is invited to the party. Marwick and her colleagues refer to this as "context collapse," and it can lead to sticky situations. In 2010, for example, Massachusetts high school administrator June Talvitie-Siple lost her job after she described students as "germ bags" and their parents as "snobby" and "arrogant" in what she said was intended to be a private Facebook post.

Even the most careful users may unintentionally give away sensitive information. As part of a class project, two engineering graduate students at MIT found that they could predict which Facebook users were gay just by looking at the sexual orientation of their online friends. "You could be completely in the closet," says sociologist Jason Kaufman, a researcher at Harvard's Berkman Center for Internet and Society. "But a savvy marketer, advertiser, blackmailer—what have you—could deduce with reasonable certainty that you're gay simply by the behavior of your friends in your network."

The privacy risks you face on Facebook are the same risks you would face in any social network, virtual or real. The Facebook experience is similar to life in a small town, in which everyone knows his or her neighbors. But a Facebook user's ability to broadcast information can easily outpace even the most energetic small-town busybody.

The heart of Facebook's information distribution system is the site's news feed, a service that aggregates updates from all the people you are connected to and displays them on a single page. Every time a user changes his or her relationship status, posts a status update, uploads a photo, or "friends" a new person, his or her other friends are all informed, virtually instantaneously.

The distance information can travel on Facebook isn't immediately apparent. The average Facebook user has 130 friends, but those friends will each have dozens or even hundreds of their own, and those friends will have their friends, and so on. "People don't understand that when you say, 'I'm making this available to friends of friends,' you're potentially opening up your network to tens of thousands of people," Marwick says.

Managing the flow of information on Facebook can be a laborious process. Facebook's software allows users to control what each friend can see, but it doesn't make it easy. Ballyamanda has to assign each new "friend" to a group. And every time she posts a status update or a new photo album, she hand selects the groups that can see it.

Many users simply aren't willing to make the effort. The privacy settings are complicated, and "just when you learn how to use the system, they go and they change it," says Amanda Nosko, a social media researcher at Wilfrid Laurier University in Waterloo, Ont., Canada.

But that doesn't mean we're headed toward Zuckerberg's open society. Rather than tailor information for different users, many Facebook users may simply self-censor, restricting how much information they share on the site.

Ballyamanda, for one, isn't about to give up her groups, despite promises from relatives that they won't use the site to spy. In a video posted to Facebook last year, Ballyamanda's aunt and uncle sit side by side and read a privacy statement that their son prepared. Her aunt, wrapped in an embroidered pink shawl, recites the words carefully in thickly accented English. "We pledge to never intrude on the privacy of our children as we embark on our journey to fully enjoy the communication benefit of Facebook," she says. "I wish to state that no one coerced us to make this statement," her uncle adds.

Her aunt and uncle seem sincere, Ballyamanda says. But it's going to take a lot more than a video to get them out of Zero Trust.

About the Author

Cassandra Willyard, a freelance writer in Brooklyn, N.Y., was intrigued to learn while reporting for "Me, Myself, or I" that Smitha Ballyamanda had arranged her Facebook friends in an elaborate hierarchy. "I should hire Smitha to organize my contacts," Willyard says. "I'd never have to worry that my editors will see me posting kitten videos when I should be working."